My Symptoms Started Yesterday. Occurred Very Suddenly And Without Warning,

My symptoms started yesterday. Occurred very suddenly and without warning, after a full nights rest I awoke still feeling the same. The symptoms I've been experiencing are: fatigue, lightheaded, dizziness, queasiness, nausea, feeling weak and more tired than usual, difficulty concentrating, upset stomach and sleepiness. This has happened before but in the past subsided by the next day. What is causing this and hie can I make it go away and prevent it from occurring again?